Converting a NEXRAD Rainfall Map into a Flood Inundation Map by ...

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Public domain digital terrain models normally have low resolution and arenot suitable for describing river channel geometry and floodplain boundaries(Werner, 2001) unless more detailed land survey studies are merged into them(Tate et al., 2002). Contours obtained from topographic surveys are a commonsource of detailed digital elevation data for local and regional studies. For theRosillo creek, a digital elevation model (ground surface model) was created fromfield surveys that generated 2-foot contour line maps (developed by contractors ofthe city of San Antonio) in the form of CAD files (.dwg, dgn, dxf) and coveringthe extent of the Rosillo creek’s floodplain. Conventional GIS Spatial Analystfunctionalities were used in this research to convert the contour line map into aDEM (raster or grid-cell representation of the surveyed terrain elevations). Thetopographic information from this land survey was also used to supply the crosssection geometric information needed for the configuration of the HEC-RAShydraulic model to ensure consistency in the analysis and in particular for theflood delineation’s final phase.3.4 FLOODPLAIN MODELINGFloodplain modeling is supported by hydrologic and hydraulic engineeringsimulations. A module for data acquisition, model execution, and modelsconnectivity is a central component of the proposed regional watershed modelingsystem.When building Flood Information Systems, a great deal of effort goes intohydrologic and hydraulic model configuration. The system proposed here uses the38
geodatabase (under Arc Hydro format) as the central data container for each ofthe included hydrologic model representations.For this research, the integration of the HEC-HMS hydrologic system(single event rainfall-runoff transformation) and the HEC-RAS hydraulic system(one-dimensional steady flow routing model) of the U.S. Army Corps ofEngineers are accomplished. In this way, this development is in tune with one ofthe two FEMA objectives for the map modernization plan, the AutomatedHydrologic and Hydraulic Engineering objective for taking advantage of newtechnology to automate mapping products of the National Flood InsuranceProgram (NFIP). In particular, the selected models for this integration (HMS andRAS) comply with the National Flood Insurance Program criteria and thus areaccepted for use in the flood hazard mapping program of the NFIP (Noman et al.,2001).Both models, HEC-HMS and HEC-RAS, with appropriate configurationsfor the Salado and Rosillo Creek respectively were provided by the engineeringdivision of the City of San Antonio. Therefore, the two models did not have to begenerated for the proposed integration as these previously generated andcalibrated models were official and available.3.4.1 Transferring Time Series to HEC-DSSOnce the precipitation records have been reassigned to the watersheds theyare transferred from geodatabase time series tables to HEC-DSS binary formatbased on the HEC-DSS Time Series Type table containing the needed arguments39
Page 3 and 4: Table of ContentsList of Figures ..
Page 5 and 6: 4.1.12 The XML2GDB Script Tool ....
Page 7 and 8: Figure 3.24 Components of a Steady
Page 9 and 10: Figure 4.50 Create Flood Inundation
Page 11 and 12: Chapter 1 Introduction1.1 BACKGROUN
Page 13 and 14: for undeveloped or natural conditio
Page 15 and 16: All the previous statements favor t
Page 17 and 18: science, and engineering models as
Page 19 and 20: Different approaches have been used
Page 21 and 22: generic and self-described formats,
Page 23 and 24: externally executed from a central
Page 25 and 26: though GIS-based, the system does n
Page 27 and 28: Geographic Information Systems, Arc
Page 29 and 30: By defining the three basic functio
Page 31 and 32: containing an inventory of damage s
Page 33 and 34: Data Models in charge of storing an
Page 35 and 36: Figure 3.1 Floodplain Modeling Sche
Page 37 and 38: either with Schematic Nodes (for Su
Page 39 and 40: channel cross sections, available H
Page 41 and 42: sequential data, called pathnames,
Page 43 and 44: Figure 3.5 NEXRAD square cells (873
Page 45 and 46: geodatabase formatted with the Arc
Page 47: The CrossSection feature class in A
Page 51 and 52: 3.4.4 External Execution of HEC-RAS
Page 53 and 54: analysis. In particular, GIS has be
Page 55 and 56: 3.5.3 Model-Specific ElementsA geog
Page 57 and 58: Figure 3.11 Geographic and Hydrolog
Page 59 and 60: For HEC-RAS, the connectivity is ac
Page 61 and 62: cross sections in the hydraulic mod
Page 63 and 64: Section line for a RAS cross-sectio
Page 65 and 66: from the geodatabase back into the
Page 67 and 68: Figure 3.19 Relationship Classes fo
Page 69 and 70: Figure 3.20 DSS Time Series content
Page 71 and 72: Figure 3.22 Extended Time Series Co
Page 73 and 74: Figure 3.23 Creating a Flow File fr
Page 75 and 76: etween the HEC-DSS file system and
Page 77 and 78: The more specific steps for the pos
Page 79 and 80: Chapter 4 Map2Map Components4.1 MOD
Page 81 and 82: A subset of NEXRAD time series data
Page 83 and 84: A folder location is also provided
Page 85 and 86: Figure 4.4 Radar2GDB Model Componen
Page 87 and 88: ecords. Figure 4.6 illustrates the
Page 89 and 90: Figure 4.8 Time Series Tables and R
Page 91 and 92: having different formats and that a
Page 93 and 94: Part E: Time Interval of stored dat
Page 95 and 96: execution time and for their corres
Page 97 and 98: on the steps needed to transfer the
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Len_sBTime (I): The length of the s
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52: Invalid precision exponent spec
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methods: user hyetograph, user gage
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Once the hyetograph is defined (for
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The resulting runoff hydrograph is
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Thus, the time period for the entir
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After the ZSRTS subroutine is execu
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Figure 4.12 HMSCaller Model Compone
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ased on a process handle (a program
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These simple command line statement
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To programmatically accomplish this
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to provide the hydraulic input for
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information into the extended Arc H
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The HydroJunction, used for connect
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Once the identification of flow cha
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As with the GDB2HMSDSS, the first t
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4.1.7 Time Series ExtractionOnce th
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accomplish this have been developed
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straight forward for all time stamp
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As opposed to HEC-DSS, the Arc Hydr
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Table 4.4: Variable Type Equivalenc
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ZCAT DSS subroutines) and stored in
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Table 4.5: Time Interval Equivalenc
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There are not specific valid values
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catalog list. For the DSS2GDB appli
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4.1.9.1 Opening the HEC-DSS fileThe
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channel (the hydraulic representati
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the model if the new configuration
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the main program as a public module
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Then, the RASCaller application acc
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Figure 4.31 ProjectName Property in
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Figure 4.33 RunSteady Method in RAS
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Figure 4.34 ExportGIS Method in RAS
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data structures delivered by every
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The two most well-known models for
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The water surface elevations obtain
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Once the water surface elevations f
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Generate a suitable water surface m
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Figure 4.42 2 Foot-Contour Lines fo
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Figure 4.43 Rosillo Creek’s terra
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standard ArcGIS tool), is used in M
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By doing this, the water surface el
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Figure 4.49 Create Flood Polygon Mo
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Int OperationThe Integer operation
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case that was developed for Map2Map
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contours (isohyetals) or by interpo
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design storm input given its possib
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Figure 4.55 Workflow for Extracting
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for it. Finally, the DigitalStorm2H
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model for water resources (Maidment
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Hydro, the HydroJunctionHasCrossSec
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involved in the transformation of r
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process model in sequence. For the
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5.6 A TRUE SPATIAL APPROACHAutomate
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time series between NEXRAD, the HEC
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value of the entire runoff hydrogra
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case study. Bigger watersheds (abov
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The first step consists in installi
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3.7 Map2Map UsageAll of the model b
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Congratulations! You have successfu
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Once the simplified version of Arc
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cells that cover your study area an
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Second, the user needs to modify th
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Appendix BMap2Map CD Content1 CD Da
Page 227 and 228:
o hmsproj - contains folders with H
Page 229 and 230:
Goodchild, M.F., Steyaert, L.T., an
Page 231 and 232:
Olsen R. J., Beling, P. A., Lambert
Page 233 and 234:
Werner, M. G. F. 2001. Impact of gr
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